Co-generation of hydrogen and carbon aerosol from coalbed methane surrogate using rotating gliding arc plasma

Highlights: • Rotating gliding arc (RGA) is proposed in coal bed methane (CBM) conversion. • The performance of CBM surrogate conversion in RGA is comprehensively evaluated. • 2D graphene sheets are formed in CBM surrogate conversion by RGA discharge. - Abstract: A novel atmospheric pressure non-thermal plasma, i.e., rotating gliding arc (RGA), is developed to upgrade coal bed methane (CBM) into hydrogen and carbon aerosol simultaneously. CH₄ is used as a CBM surrogate. In present work, the V-I characteristics of RGA discharge in CH₄ conversion are monitored with different gases (N₂, Ar and CO₂) as carrier gas, while the active species (such as OH, CH, CN, C₂, excited molecules and ions) involved in the plasma reactions are identified by optical emission spectroscopy (OES). According to the sensitivity analysis of specific energy density (SED), the importance of operating conditions on SED sensitivity is in a sequence of CH₄ concentration > applied voltage > residence time. The performance of CH₄ conversions are comparatively evaluated based on the variation of operating conditions. In general, the enhancement of applied voltage and residence time effectively increases the CH₄ conversions, selectivity of hydrogen, as well as the energy efficiency, while the augment of CH₄ concentration has a negative effect in contrast. The carbon aerosol obtained in CH₄/N₂ and CH₄/Ar discharge are comparatively investigated. Transparent crumped-like graphene sheets and spherical nanostructure carbon are observed in both obtained carbon aerosol, with relative high I_D/I_G ratios (∼0.62) indicated in Raman spectroscopy. High C/O ratios (>14) are obtained in the XPS survey spectra, with the intensity ratios of sp² C=C/sp³ C-C occupy about 80%. However, the BET surface area of carbon obtained from CH₄/N₂ is almost 3 times larger than that from CH₄/Ar discharge. In addition, super hydrophobic and oleophilic properties are observed in both carbon samples. The contact angles of water droplets are above 130°, while the contact angle of oil is less than 4°.